Solving the riddle of data storage with iSCSI

Howard Marks, Contributor

The most reliably true statement in the world of computing is that data grows to fill all available space. For those running Windows server farms, iSCSI is an increasingly popular storage option to deal with the crunch.

The most reliably true statement in the world of computing is that data grows to fill all available space. As a result, those of us who run Windows server farms stay busy trying to keep up with it all.

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We buy as much disk as a server will hold when we buy a new server but, eventually, the fact that senior vice presidents just won't clean out their mailboxes catches up with us.

We try to keep as much data as possible on a big honking file server or network-attached storage (NAS) box, but some platforms, like Exchange and SQL server, just won't store their data on file servers and NAS boxes. SQL server won't even let you dump a database for backup to a remote file share. Combine this with the need for 50% free disk space to rebuild a database, and we have storage all over and a shortage at the same time.

The traditional solution to this problem is a Fibre Channel Storage Area Network (SAN). In the SAN environment your servers can share a single pool of available storage, so you can allocate space to the servers as they need it. Therefore, you can expand existing logical drives and/or allocate temporary ones and return the space to the free pool when you're done with it.

The most obvious problem with Fibre Channel is cost. To hook a server into a Fibre Channel SAN, you would need a $1,000 host bus adapter (HBA) and a Fibre Channel switch that will set you back $800 to $4,000 a port. If that isn't bad enough, once you decide to take the plunge, you'll discover that in Fibre Channel networking you can't just plug vendor A's HBA into your server to talk to vendor B's disk array through Vendor C's switch. Fibre Channel interoperabity is an iffy thing. If your entire SAN isn't on a vendor's hardware compatibility list, you may never get it working.

Now more than two years old, iSCSI lets you build SANs without the cost and complexity of Fibre Channel. It wraps the SCSI common command set in good old TCP/IP. Standard TCP/IP as a protocol means you can use standard gigabit Ethernet as the transport protocol connecting servers to disk arrays with the same Cat5 cable and switches you know and love.

Does bandwidth equal performance?

The Fibre Channel camp will tell you that you get what you pay for and that today's Fibre Channel equipment is, at 2 gigabytes per second, twice as fast as gigabit Ethernet. And, at next year's 4 GBps, FC gear will be four times as fast as iSCSI on gigabit Ethernet. This is a typical mischaracterization of bandwidth for speed. The RAID array, not the connection speed, determines the performance for most applications. After all, the PCI-X bus in most Windows servers can only handle 1 GBps.

All you need to build an iSCSI SAN is a Gigabit Ethernet switch, an iSCSI disk array to act as the target and Microsoft's iSCSI Initiator for Windows server, which is a free download from the Microsoft Web site. At least a dozen vendors now sell iSCSI disk arrays ranging from standard Intel servers with ATA drives running an iSCSI target in software to iSCSI versions of EMC Corp.'s midrange CLARiiON CX series.

If you have a spare Windows server and want to see how iSCSI might fit in your environment, you can download a 14-day evaluation copy of String Bean Software Inc.'s WinTarget and turn it into an iSCSI target.

Once you have a SAN, you can build and allocate logical drives to your various servers, grow them dynamically and enjoy the peace of mind of being able to allocate disk space when you need it. Sure beats spending the weekend adding an external SCSI cabinet to the Exchange server, doesn't it?

Howard Marks has been in the personal computer industry from the very beginning. Starting at Lifeboat Associates in 1979, he founded Networks Are Our Lives in 1981 as a builder of custom single- and multi-user CP/M computers. Today, NAOL focuses on network design and documentation, storage consolidation and management projects, and it generally helps organizations clean up their network messes.

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